The present invention relates generally to a logging tool conveyance system, and more particularly, to a method and apparatus for conveying a logging tool through an earth formation traversed by a horizontal or highly deviated borehole.
To economically produce hydrocarbons from a reservoir, it has become increasingly common to drill a borehole, through an earth formation, which deviates from the traditional vertical orientation. The deviation may result from drilling a borehole using either a sharp or gradually increasing angle away from the vertical axis. The deviation may also result from drilling a borehole which extends horizontally from the vertical axis. It is well known in the art to attempt the logging of formations surrounding such deviated or horizontal boreholes with logging tools lowered into the wellbore on a wireline and/or a cable. Such tools usually depend upon the force of gravity to permit positioning of the tool within the borehole. However, when the borehole is drilled at a sufficiently high angle, the force of gravity on the tool and wireline is insufficient to overcome the friction encountered by the tool and wireline against the highly deviated portion of the borehole wall. Stiff devices, such as drill pipe and coiled tubing, have been used for conveyance of logging tools in horizontal and highly deviated boreholes. Often times, many hours of work are required to convey logging tools in this fashion. Furthermore, coiled tubing conveyance is limited in reach due to helical buckling. Thus, it has become essential to provide an economical and expedient means of conveying a logging tool through the horizontal or highly deviated portion of a borehole.